According to Kotaku, Bethesda has intent to begin a lawsuit with Interplay over Fallout Online as sourced from Interplay legal documents. According to the article, Bethesda set stipulations for allowing Interplay to use the license which apperently Interplay didn't cooperate with too awful well.
Of these stipulations, it seems the major one is that Interplay had to have began "full-scale" work on the title by April 4th, 2009 as well as Interplay apperently not securing finicial . Should this reach court and Interplay loses, they will lose rights to the Fallout MMO and Fallout will forever remain Bethesda's sole property.
I'm not so sure who I should cheer for in this one.
You can read more at Kotaku: here, including the court papers if you feel the need to add some legalese to spice up your vocabulary.